A waterproof fabric comprising a base fabric with a resin coating thereon, especially a moisture (water vapor) permeable waterproof resin coating has been used in a broad range of clothes, for example, sport clothes such as windcheaters, waterproof work wear for use in rainy weather, and waterproof uniforms (coats and loose jackets). These uses take advantage of the moisture permeability and waterproof properties of the waterproof coated fabric.
A waterproof garment made of waterproof fabric is, in general, produced by joining cloth pieces, which are cut to desired shape from a waterproof fabric, together into a welt seam (to give a decorative effect and to prevent seam catching or so called mimesis) by sewing, and thereafter laminating a sealing tape on the inner side of the welt seam portion. For this reason, there is encountered a problem in which the seamed portion of the garment becomes exceedingly less waterproof than the waterproof fabric material itself.
Further, a sealing tape cannot be applied in the prior art unless a garment is made of a fabric constructed of a small denier filamentary yarn. This is because an expected waterproof property cannot be obtained when a sealing tape is applied to the fiber surface of the base fabric of a waterproof fabric with a resin coating on its right side, especially when the base fabric of a waterproof fabric is a knitted fabric such as tricot which is made of a large denier filamentary yarn or spun yarn made of staple fiber.
In case where a sealing tape is applied onto the back side of a waterproof fabric, the joining seam portion becomes stiff due to both the application of the sealing tape and lack of close contact between the sealing tape and the base fabric.
Still another drawback encountered in the application of sealing tape is that a joining seam may cause an insufficiency in waterproof property when a sealing tape is readily buckled or poorly disposed, off the run of stitches, due to the presence of a bent or curved run of stitches in a seam structure. Accordingly, use of straight-line stitching has been the only way to avoid an occurrence of buckling and/or slipping-off of sealing tape over the stitching line. Use of a straight line stitching, however, greatly restricts the possible range of garment design.
In the manufacturing clothes such as sport clothes such as windcheaters and the like, rain wear, waterproof work wear from a waterproof fabric composed of a base fabric and thermoplastic resin film layer, it has been known that high-frequency welder, an ultra-sonic welder and the like have been used for obtaining a joining bond free from sewing stitches between overlapping faces of base fabrics, with or without the use of adhesive, in order to prevent joining interfaces of fabrics (or cloths) being penetrated by water.
These known methods of joining by means of a welded bond by a high-frequency welder can produce waterproof joining bonds in which the waterproof property is maintained only at an early stage of their use. However, joining bonds obtainable by the known method of melt adhesion bonding gives, on the whole, relative low bond strengths when being compared with those of joining seams obtained by sewing. Besides, the joining bonds by the known methods tend to be stiff and easily damaged and/or split, therefore they have a drawback in durability of the waterproof properties under repetitive use over a long time.
An improved method for obtaining a joining structure both waterproof and strong is proposed, for example, in Japanese Examined Utility Model Publication No. 62-24516 in which formation of a strong joining structure obtained by sewing with use of sewing thread is followed by an application of a high-frequency welding. FIG. 13 illustrates a cross-section view of a waterproof joining structure described in the above-mentioned known art. In the figure, there is shown a joining structure comprising a two pieces (B.sub.1) and (B.sub.2) of waterproof fabrics in which the top waterproof layers (5a) and (5b) of a thermoplastic synthetic resin, for example, vinylchloride, are coated on each one faces of the base fabric layers (10) of the waterproof fabric pieces (B.sub.1) and (B.sub.2). The top surface of waterproof layers (5a) and (5b) of waterproof fabric pieces (B.sub.1) and (B.sub.2) are laid one over the other, on which a piece of thermoplastic adhesion bonding tape (6) is disposed. A set of these layers en bloc is, then, sewn together along the marginal end with a sewing thread (7), and then piece (B.sub.1) of the waterproof fabric, which is in contact with the above-mentioned adhesion bonding tape (6), is folded back over the top face of the adhesion bonding tape. The folded structure en bloc is then heated by pressing by means of an electrode plate (a) to form a waterproof joining structure of a waterproof fabric in which waterproof layers (5a) and (5b) and adhesion bonding tape (6) are bonded by hot press adhesion.
The method explained above can produce a joining structure having a bonding strength of greater than 25 kg/2.5 cm width with improved durability. However, the joining structure has a tendency to deteriorate at the melt-binding portion of waterproof layers (5a) and (5b) and that an irregularity in the thickness of the joining structure is easily produced, since the waterproof layers of waterproof fabric and the heat welding tape are melted to form a press mark (a') of the mold of high-frequency welder on the surface of the waterproof fabric. Further, the joining structure is stiff to the touch (the bending resistance in terms of bending modulus exceeds 20 gf.multidot.cm.sup.2 /cm) as well as a tendency to be easily cracked and/or split (water resistance of a specimen after being rubbed 1,000 times according to Scott shape method: not greater than 800 mm H.sub.2 O). Besides, it has been observed that the joining structure is not easy to fit to a wearer's body and lacks a property of dynamic fitability (following-up the wearer's body motion). For this reason, the known method mentioned above cannot produce waterproof fabric having properties satisfying both waterproof and joining bond properties.
Japanese Examined Utility Model Publication No. 61 (1986)-31749 discloses that a method of sealing a seam portion in which a piece of a sheet capable of developing foam is joined together between a pair of pieces of fabric by a sewing thread and is heated to generate foam in the sheet. According to the method, the sheet is forced to grow 10 fold (3 to 4 fold as large in the examples) as large as its original size by blowing with the use of blowing agent so that the needle holes can be sealed to a certain degree. It does, improve the waterproof properties because needle holes filled with the porous material have a low resistance to water. Further, the seam structure can be readily deformed due to an increased thickness of the seam portion and the shape of the seam portion lacks a property of dynamic fitability (following-up the wearer's body motion). As a result, the method cannot produce a seam structure which satisfies the durability requirement for waterproofness and resistance to water under a prolonged use, especially in case where clothes are worn for a long time. In addition, a problem of deterioration of the waterproof layer due to heat treatment by external heating means occurs.
In Japanese Unexamined Patent Publication No. 6 (1994)-246076, there is described a method for forming a joining seam structure for waterproof cloths exhibiting a water resistance at a level required for an umbrella fabric in which the cloths are made of a moisture permeable waterproof fabric composed of a thermoplastic resin layer coated on one face of the base fabric having a water resistance greater than 500 mm H.sub.2 O. As described in the publication, the known joining structure has a water resistance of about 500 mm H.sub.2 O and is produced by making a joining structure containing a welt seam comprising a combweb like spun fiber web tape, or film of a hot melt resin having a basis weight of about 30 to 100 g/m.sup.2 interposed along a stitching line between an overlap of a waterproof fabrics, and thereafter melting the hot melt resin so that a joining structure having a water resistance of about 500 mm H.sub.2 O is formed.